Visible-Light-Induced, Catalyst-Free Radical Arylations of Arenes and Heteroarenes with Aryldiazonium Salts

In the absence of a photocatalyst and other additives, the radical arylation of diverse arenes and heteroarenes has been achieved with aryldiazonium salts under visible-light irradiation from a blue light-emitting diode (LED). Although the course of some reactions can be rationalized by the formation of strongly light-absorbing charge-transfer (CT) complexes between the diazonium ion and the aromatic substrate, several further examples indicated that the simple presence of an aromatic substrate, showing only weak interactions to the diazonium ion, is fully sufficient to enable product formation.